Difference between 2 lines of 2 differents cross table

[GuiCoRe]

Dear All,
First i'm using Cognos BI 10.1 report studio & SQL Server.

I have 2 cross table (see in attachement), which contains a line call "total" which is the total of all dynamic lines (Elements of line are prompted).
Both cross table are using the same table (but differents requests) to display datas, only the line are dynamics (choose by the users).
So, 2 requests on the same table with different filter.

I'm trying to have another cross table with the difference of the lines total ( in the printscreen, it should be total1-total2) with the same columns.
Can you help me about this ?

I precise that I use relationnal datas.

Thank you for your help,
GuiCoRe